1. Field of the Invention
The present invention relates to an electronic musical instrument of the type that accumulates phase angle data corresponding to keys being depressed and utilizes the accumulated output for accessing a waveform memory to read out therefrom musical waveform data.
2. Description of the Prior Art
Heretofore there has been used widely an electronic musical instrument of the type that accumulates phase angle data corresponding to keys being depressed and utilizes the accumulated output for accessing a waveform memory to read out therefrom waveform data of a musical frequency. The electronic musical instrument of this type employs a method of adding up the phase angle data and difference phase angle data of a little different pitch for generating a pitch-shifted frequency. This method does not matter, in principle, because it is merely a simple addition of different pieces of data. However, this method calls for an adder therefor, and hence increases the scale of the whole circuit structure, introducing difficulty in the fabrication of the circuit as a one-chip large scale integrated circuit.
FIG. 4 shows a prior art example. In FIG. 4, the output of a phase angle memory 101, which stored phase angle data .omega.1 for determining the fundamental frequency, and the output of a phase angle memory 102, which stores difference phase angle data .DELTA..omega.2 for determining a pitch-shifted frequency, are added up by an adder 103, providing phase angle data .omega.1+.DELTA..omega.2. This output is accumulated sequentially at a certain sampling clock by means of an accumulator 107 composed of an adder 104 and a register 105. The accumulator 107 outputs frequency data F=F+(.omega.1+.DELTA..omega.2), which is applied as an address to a wave-form memory 106, reading out therefrom waveform data of a pitch shifted from the fundamental frequency.
The prior art example employs the method that involves the calculations (1) .omega.=.omega.1+.DELTA..omega.2 and (2) F=F+.omega., and its circuit calls for many bus lines because the term including .omega. is needed in the circuit of each stage forming the whole system.
The present inventor has noticed, as a solution to this problem, that different frequencies could easily be generated simply by performing two accumulations (1) f=f+.omega.1 and (2) f=f+.DELTA..omega.2 by the same accumulator while controlling the calculation cycle.